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1922 


UNITED  STATES  DEPARTMENT  T)F  AGRICULTURE 


BULLETIN  No.  342 


Washington,  D.  C. 


Issued  January  8,  1916;  revised  October  10, 1922 


THE  PRESENT  STATUS  OF  THE  PASTEURIZATION 

OF  MILK. 


By  S.  HENRY  AYERS, 
Bacteriologist,  Dairy  Division,  Bureau  of  Ani, 


CONTENTS. 


Meaning  of  the  term  pasteurization- 
Value   of  pasteurization 

Electrical  and  ultra-violet-ray  treat- 
ment of  milk 

Extent     of     pasteurization     in     the 

United    States 

Methods  of  pasteurization 

Advantages  of  low-temperature  pas- 
teurization   

Temperatures  and  methods  most  suit- 
able for  pasteurization 

Supervision  of  the  process 


B 

7 

10 

11 
33 


Handling  milk  after  pasteurization- 

Cost  of  pasteurizing  milk 

Bacteria    which    survive    pasteuriza- 
tion   

The  colon  test  for  efficiency  of  pas- 
teurization   

Past  and  present  theories  of  pasteur- 
ization   

Pasteurization  and  vitamins 

The  necessity  for  pasteurization 

References  to  literature-— 


15 
16 

16 

20 

20 
22 
24 
25 


MEANING  OF  THE  TERM  PASTEURIZATION. 

The  term  "pasteurization"  originated  from  the  experiments  of 
Louis  Pasteur,  in  France.  From  1860  to  1864,  in  experiments  on  the 
u  diseases "  of  wine,  he  found  that  heating  for  a  few  moments  at 
temperatures  of  from  122°  to  140°  F.  was  sufficient  to  prevent  abnor- 
mal fermentations  and  souring  in  wine.  A  little  later  he  found 
that  by  a  similar  heating  beer  could  be  preserved  from  souring. 
The  application  of  the  process  gave  rise  to  the  term  "  pasteurization." 
As  applied  under  commercial  conditions,  pasteurization  is  the  process 
of  heating  for  a  short  or  a  long  period,  as  the  different  processes 
demand,  at  temperatures  usually  between  140°  and  185°  F.  As  ap- 
plied to  milk  for  direct  consumption,  pasteurization  should  mean 
a  process  of  heating  to  145°  F.  and  holding  at  that  temperature  for 
30  minutes.  The  process  is  followed  by  rapid  cooling. 

elieved  that  the  term  pasteurization  should  be  applied  only 
ocess  of  heating  at  145°  F.  for  a  period  of  30  minutes. 

.48°— 22 1 


4933 


DEPARTMENT  OF  AGRICULTURE. 

PASTEURIZATION. 


From  a  sanitary  standpoint,  the  value  of  pasteurization  is  of 
greatest  importance  when  market  milk  is  under  consideration.  The 
pasteurization  of  milk,  when  the  process  is  properly  performed, 
affords  protection  from  pathogenic  organisms.  Such  disease-pro- 
ducing bacteria  as  Bacillus  tuberculosis  ,  B.  diphtherias,  B.  typhi, 
and  other  organisms  of  the  typhoid-paratyphoid  group,  and  the 
dysentery  bacillus,  when  heated  at  140°  F.  for  20  minutes  or  more 
are  destroyed,  or  at  least  lose  their  ability  to  produce  disease. 

Occasionally  results  are  reported,  such  as  those  of  Twiss  (30),1 
which  again  open  the  question  as  to  the  destruction  of  certain  patho- 
genic organisms  by  pasteurization.  Using  test  organisms  of  the 
typhoid-paratyphoid  group,  she  obtained  results  which  indicated 
that  there  was  not  a  complete  destruction  of  these  organisms  when 
heated  in  milk  at  140°  F.  and  even  at  149°  F.  for  30  minutes.  Krum- 
wiede  and  Noble  (24)  ,  however,  using  some  of  the  same  test  organ- 
isms of  the  typhoid-paratyphoid  group  as  used  by  Twiss,  found  that 
they  did  not  survive  heating  for  10  minutes  at  140°  F.  They  further 
pointed  out  that  the  apparent  heat  resistance  of  the  strains  used  by 
Twiss  was  due  to  the  method  of  determining  their  thermal  death 
point. 

According  to  Mohler  (25),  pasteurization  offers  protection  against 
foot-and-mouth  disease.  He  makes  the  following  statement  : 

Milk  which  has  been  pasteurized  for  the  elimination  of  tubercle  and  typhoid 
bacilli  will  not  prove  capable  of  transmitting  the  disease  (foot-and-mouth)  to 
persons  or  animals  fed  with  it. 

In  view  of  the  outbreak  of  foot-and-mouth  disease  in  this  country 
a  few  years  ago  this  statement  is  of  importance. 

The  abortuslike  bacteria  in  the  udders  of  healthy  cows  which  were 
demonstrated  by  Evans  (15)  may  also  be  considered  in  a  discussion 
of  pasteurization.  Although  their  sanitary  significance  has  not  been 
definitely  established,  it  is  interesting  to  observe  that  it  was  found 
by  Evans  (16)  that  both  the  pathogenic  and  lipolytic  varieties  could 
be  destroyed  by  heating  to  125°  F.  for  30  minutes  or  to  145°  F.  for 
30  seconds. 

Within  recent  years  several  epidemics  of  septic  sore  throat  have 
been  traced  to  milk.  In  some  of  these  epidemics  it  was  found 
possible,  by  pasteurization,  to  destroy  streptococci  which  were  iso- 
lated from  throats  of  infected  people  and  which  were  believed  to 
be  the  infective  agents.  Pasteurization,  properly  performed,  seems 
to  protect  against  epidemics  of  this  kind,  but  until  the  organism 


'See  References  to  literature. 


STATUS  OF  PASTEURIZATION   01    ^XIJxA.  3 


which  causes  the  disease  is  definitely  knpwij.it  is  imp-^ssjljje.  i<;  say 
that  it  affords  absolute  protection. 

Since  it  is  quite  generally  believed  that  the  streptococci  are  the 
causative  agents  of  septic  sore  throat,  the  ability  of  certain  of  this 
group  of  organisms  to  stand  temperatures  above  that  of  pasteuriza- 
tion naturally  presents  a  grave  situation.  If  pathogenic  streptococci 
are  able  to  survive  the  usual  process  of  pasteurization,  the  value  of 
the  process,  from  a  sanitary  standpoint,  is  materially  lowered. 

Experience  with  the  use  of  properly  pasteurized  milk  and  the  de- 
termination of  the  thermal  death  point  of  pathogenic  streptococci 
by  various  investigators  indicate  very  clearly,  however,  that  the 
thermal  death  point  of  these  organisms  is  relatively  low  and  that 
they  are  readily  destroyed  by  proper  pasteurization.  Thus  Ham- 
burger (IT),  who  studied  the  epidemic  of  septic  sore  throat  in 
Baltimore  in  1912,  traced  this  epidemic  to  a  certain  milk  supply. 
Advice  was  given  to  boil  all  milk,  and  the  dairy  connected  with 
the  epidemic  raised  the  temperature  of  its  flash  pasteurization  to 
160°  F.  ;  then  it  changed  to  the  holder  process  by  which  the  milk 
was  heated  to  145°  F.  and  held  for  a  period  of  30  minutes.  The 
cases  of  sore  throat  that  followed  were  neither  so  severe  nor  so 
numerous  and  did  not  follow  the  milk  supply,  but  appeared  to 
have  been  transmitted  from  individual  to  individual.  Hamburger 
(18)  also  found  that  a  streptococcus  isolated  from  a  patient  having 
a  case  of  sore  throat  was  killed  by  heating  in  milk  at  145°  F.  for 
30  minutes. 

Again,  Capps  and  Miller  (12)  who  studied  the  Chicago  epi- 
demic of  septic  sore  throat,  traced  it  to  a  dairy  where  the  milk  was 
pasteurized  by  the  flash  process  at  160°  F.  On  certain  dates  they 
found  that  there  was  a  pronounced  failure  to  pasteurize  and  follow- 
ing these  dates  there  were  outbreaks  of  septic  sore  throat.  These 
authors  believed  that  the  final  responsibility  for  the  epidemic  rested 
on  the  inadequate  and  unreliable  pasteurization.  They  state  that 
the  absolute  protection  of  the  children  of  the  Michael  Reese  Hos- 
pital from  infection  by  efficient  pasteurization  demonstrates  this 
point.  Bray  (11),  who  studied  an  epidemic  of  tonsillitis  of  tuber- 
culous patients,  traced  the  epidemic  to  a  milk  supply  of  one  farm 
where  a  carrier  presumably  infected  the  milk.  Forty  cases  of 
tonsillitis  resulted  among  400  people.  As  soon  as  the  epidemic 
broke  out  the  milk  was  pasteurized,  and  from  that  time  only  1 
case  appeared. 

From  the  results  achieved  from  the  proper  pasteurization  of  milk 
it  seems  evident  that  the  thermal  death  point  of  pathogenic  strep- 
tococci, which  cause  septic  sore  throat,  is  relatively  low.  This  belief 


BULLETIN/  3a2j:U,.:S.   DEPARTMENT  OF  AGRICULTURE. 


is  bo^^oi^by.-'tliEesiXite-O'f  the  studies  of  Davis  (13),  who  found 
that  streptococci  isolated  from  cases  of  sore  throat  were  readily  killed 
by  heating  at  140°  F.  for  30  minutes.  He  also  found  that  none  of  24 
strains  of  pathogenic  hemolytic  streptococci  of  human  origin  resisted 
heating  at  140°  F.  for  30  minutes.  He  makes  the  following  statement  : 

I  know  of  no  evidence  that  strains  of  streptococci  pathogenic  to  man  can  resist 
the  usual  temperature  of  pasteurization,  145°  F.,  for  30  minutes. 

Further  evidence  that  pathogenic  streptococci  are  destroyed  by 
proper  pasteurization  was  presented  by  the  results  obtained  by  Ayers, 
Johnson,  and  Davis  (7),  who  found  that  27  strains  of  these  organisms 
were  always  destroyed  by  heating  at  140°  F.  for  30  minutes. 

Epidemics  of  scarlet  fever  have  been  traced  to  milk  supplies,  and 
in  such  cases  pasteurization  has  been  resorted  to,  with  apparently 
satisfactory  results,  as  a  means  of  safeguarding  the  public  health. 

Pasteurization  is  of  value  from  a  commercial  standpoint  so  far  as 
it  increases  the  keeping  quality  of  the  milk  and  assists  in  preventing 
financial  losses  by  souring.  As  practiced  at  the  present  time,  commer- 
cial pasteurization,  with  reasonable  care,  destroys  about  99  per  cent 
of  the  bacteria  (this  percentage  varies,  depending  upon  the  propor- 
tion of  heat-resistant  bacteria  in  the  milk),  and  while  it  does  not 
prevent  the  ultimate  souring  of  milk,  it  does  delay  the  process.  At 
the  present  time  pasteurization  is  the  best  process  for  the  destruction 
of  bacteria  in  milk  on  a  commercial  scale. 

ELECTRICAL    AND    ULTRA-VIOLET-RAY    TREATMENT    OF    MILK. 

Many  attempts  have  been  made  to  destroy  bacteria  in  milk  by 
means  of  electricity,  but  no  process  has  been  devised  which  has  been 
commercially  applied  to  any  great  extent. 

Alternating  currents  have  been  most  extensively  worked  with,  be- 
cause direct  currents  were  found  to  produce  undesirable  chemical 
changes  in  milk.  While  the  proper  application  of  suitable  alternating 
currents  has  resulted  in  bacteria  reductions  similar  to  those  produced 
by  pasteurization,  it  appears  to  be  an  open  question  as  to  whether 
the  action  of  the  electric  current  is  due  to  the  heat  generated  or  to 
the  direct  action  of  electricity  on  the  bacterial  cells. 

Thornton  (28),  who  studied  this  question  in  England,  came  to  the 
conclusion  that  the  destruction  of  bacteria  must  be  regarded  as  due 
largely  to  thermal  changes  rather  than  electrical,  but  thought  his 
results  indicated  some  electrical  action  on  the  molecular  structure  of 
the  bacteria.  Beattie  (8,  9),  also  working  in  England  on  the  same 
problem,  came  to  the  conclusion  that  heat  was  not  the  principal  fac- 
tor in  the  destruction  of  bacteria  by  electricity,  but  found  that  to 
obtain  satisfactory  results  the  temperature  should  not  be  below  145° 


STATUS   OF   PASTEURIZATION   OF   MILK.  5 

F.  In  the  United  States  an  electric  process  has  been  investigated  by 
Anderson  and  Finkelstein  (1).  Their  conclusion  as  to  the  cause  of 
the  destruction  of  the  bacteria  is  as  follows : 

The  destruction  of  bacteria  in  the  " "  process  is  apparently  due  to 

the  heat  produced  by  the  electric  current  rather  than  to  the  electric  current 

itself.     The    " "    process    furnishes    a    method    for    producing    a    very 

sudden  high  temperature  for  a  brief  period  of  time. 

It  seems  evident  from  a  review  of  the  literature  that  in  the  use  of 
electricity,  as  it  has  been  applied,  sufficient  heat  is  generated  by  elec- 
tricity, or  a  combination  of  steam  and  electricity,  to  raise  the  milk 
to  the  pasteurizing  temperature.  Since  the  temperatures  reached 
are  in  themselves  destructive  to  most  nonspore-forming  bacteria, 
the  problem  of  determining  whether  the  effect  of  electricity  is  due 
to  heat  or  direct  electric  action  is  a  difficult  one. 

The  use  of  ultra-violet  rays  for  the  destruction  of  bacteria  in  milk 
has  not  proved  to  be  of  value  as  a  commercial  process.  Experiments 
with  these  rays  carried  on  by  Ayers  and  Johnston  (5)  showed  that 
while  the  rays  cause  great  destruction  of  bacteria  in  milk,  when  ex- 
posed under  suitable  conditions,  the  process  in  its  present  state  of 
development  can  not  replace  that  of  pasteurization  on  a  commercial 
scale.  It  is  difficult  to  obtain  the  proper  exposure  of  milk  to  the 
rays  on  a  scale  sufficient  to  permit  of  practical  operation  and  im- 
practicable to  secure  suitable  bacteria  reductions  without  seriously 
injuring  the  flavor  of  the  milk. 

EXTENT  OF  PASTEURIZATION  IN  THE  UNITED  STATES. 

Pasteurization  when  first  practiced  by  milk  dealers  in  this  country 
was  carried  on  more  or  less  secretly,  and,  except  as  a  means  of  pre- 
serving the  milk,  was  regarded  by  them  as  a  process  of  no  value.  As 
the  practice  became  more  general  the  subject  of  pasteurization  was 
studied,  and  its  value  as  a  means  of  destroying  disease-producing 
bacteria  was  recognized.  In  consequence  of  the  recognition  of  the 
merits  of  the  process  there  has  been  during  the  last  20  years  a  rapid 
increase  in  the  quantity  of  milk  pasteurized.  Jordan  (23) ,  in  a  paper 
published  in  1913.  stated  that  10  years  previously  only  about  5  per 
cent  of  the  milk  supply  of  Xew  York  City  was  pasteurized ;  figures 
from  other  sources  show  that  about  40  per  cent  in  1912,  88  per  cent 
in  1914,  and  98  per  cent  in  1921  was  pasteurized.  In  Boston  very 
little  milk  was  pasteurized  in  1902,  but  in  1915  80  per  cent,  while  at 
present  about  90  per  cent  is  so  treated.  In  many  of  the  smaller  cities 
there  have  been  corresponding  increases  in  the  quantity  of  milk 
pasteurized  during  the  last  few  years. 

The  general  tendency  in  this  country  to-day  is  toward  the  pasteuri- 
zation of  all  milk  for  direct  consumption,  with  the  exception  of 


BULLETIN  342,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 


certified  or  equivalent  grades  of  milk  from  tuberculin-tested  herds. 
Some  idea  of  the  increase  in  the  extent  of  pasteurization  in  the  United 
States  from  1915  to  1921  may  be  gained  by  a  study  of  Table  1.  The 
figures  were  obtained  from  a  questionnaire  sent  to  health  officers.  In 
1915  the  figures  were  based  on  344  replies  and  379  in  1921. 

TABLE  1. — Extent  of  pasteurization  of  milk  in  cities  m  the  United  States  of 
more  than  10,000  population  in  1915  and  1921. 


Population  of 

Number  of 
cities 
answering. 

50  per  cent 
or  more 
pasteurized. 

10  to  50  per  cent 
pasteurized. 

0  to  10  per  cent 
pasteurized. 

None 
pasteurized. 

cities. 

1915 

1921 

1915 

1921 

1915 

1921 

1915 

1921 

1915 

1921 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

Perct. 

More  than  500,000.   . 
100,001  to  500,000.  .   . 

9 
40 

12 
42 

77.8 
30.0 

100.0 
90.5 

22.2 
50.0 

0 
9.5 

0 
15.0 

0 
0 

0 
5.0 

0 
0 

75,001  to  100,000...  . 
50,001  to  75,000  

19 
30 

15 
34 

26.3 
12.3 

73.3 

67.7 

42.1 
50.0 

26.7 
14.7 

21.0 
20.0 

0 
2.9 

10.6 
16.7 

0 
14.7 

25,001  to  50,000  

78 

62 

16.7 

59.7 

39.7 

25.8 

15.4 

3.2 

28.2 

11.3 

10,001  to  25,000  

168 

126 

6.0 

33.3 

23.8 

18.3 

10.7 

9.5 

59.5 

38.9 

It  will  be  noted  that  since  1915  there  has  been  a  great  increase  in 
the  percentage  of  cities  in  which  more  than  50  per  cent  of  the  milk 
is  pasteurized.  There  has  been  during  the  same  period  a  marked 
decrease  in  the  percentage  of  cities  having  no  pasteurized  milk. 

Table  1  does  not  contain  any  data  from  cities  of  less  than  10,000 
population,  but  replies  from  88  such  cities  showed  the  following 
figures :  In  22  cities  50  per  cent  or  more  of  the  milk  was  pasteurized, 
in  12  others  from  11  to  50  per  cent,  and  in  two  cities  10  per  cent 
or  less  was  so  treated.  Fifty-two  of  the  88  cities  reported  no  pas- 
teurized milk.  It  seems  evident,  therefore,  that  the  process  of  pas- 
teurization is  being  used  extensively  in  this  country  even  in  the 
small  cities. 

A  study  of  the  available  figures  on  the  extent  of  pasteurization 
revealed  a  few  more  facts  which  may  be  of  interest.  In  1915  milk 
was  pasteurized  in  about  62  per  cent  of  the  cities  with  a  population 
above  10,000,  and  in  1921  in  about  80  per  cent  of  such  cities.  The 
increase  in  pasteurization  in  small  cities,  10,000  to  25,000,  is  shown 
by  the  fact  that  in  1915  about  40  per  cent  of  these  cities  reported 
pasteurized  milk  compared  with  approximately  61  per  cent  in  1921. 

Considering  these  figures  as  a  whole  the  increasing  trend  of  pas- 
teurization is  plain. 

A  good  idea  of  the  present  extent  of  pasteurization  may  be 
obtained  from  Table  2.  It  will  be  observed  that  there  is  an  increas- 
ing tendency,  which  follows  their  increasing  population,  for  cities 
to  have  pasteurized  milk  and  also  to  pasteurize  a  higher  percentage 
of  the  supply. 


STATUS  OF  PASTEURIZATION   OF   MILK. 


TABLE  2.— Proportion  of  cittes  having  pasteurized  milk  and  average  per  cent  of 
their  milk  supply  ichich  VMS  pasteurized  in  1921. 


Number  of 

Number  of 

Per  cent 

Average 

cities 

cities 

of  cities 

percent 

Population  of  cities. 

reporting 
pasteur- 
ized milk. 

with  no 
pasteur- 
ized milk. 

with 
pasteur- 
ized milk. 

of  milk 
pasteur- 
ized. 

More  than  500  000                                 

12 

0 

100 

95 

100  001  to  500  000 

42 

0 

100 

72 

75  001  to  100  000 

15 

0 

100 

68 

50'001  to  75  000                                                          ... 

29 

5 

85 

65 

25  001  to  50  000 

55 

7 

89 

58 

10  000  to  25,000     .                               

77 

49 

61 

51 

Less  than  10,000  

36 

52 

41 

53 

Total 

266 

113 

For  those  who  are  particularly  interested  in  the  quantity  of  milk 
pasteurized  in  various  cities,  Table  3  has  been  prepared.  In  it  is  a 
list  of  266  cities  that  reported  pasteurized  milk  and  the  approxi- 
mate quantity  of  milk  pasteurized.  The  cities  are  listed  in  order  of 
their  population  given  in  the  1920  census  and  include  all  cities  re- 
porting pasteurization  up  to  the  time  the  table  was  prepared.  It  is 
particularly  interesting  to  note  the  extent  to  which  milk  is 
pasteurized  even  in  the  small  cities. 

METHODS  OF  PASTEURIZATION. 

At  present  three  processes  of  pasteurization  are  practiced  in  this 
country.  The  first  is  known  as  the  flash,  or  continuous  process;  the 
second,  the  holder,  or  holding  process;  and  the  third  is  known  as 
pasteurization  in  the  bottle. 

TABLE  3. — Approximate  quantity  of  milk  pasteurized  in  various  cities  as  shown 
by  returns  from  questionnaire  sent  in  1921. 


City. 

Popula- 
tion, 1920 
census. 

Per  cent 
of  milk 
pas- 
teurized. 

City. 

Popula- 
tion, 1920 
census. 

Per  cent 
of  milk 
pas- 
teurized. 

New  York  N  Y 

5  620  048 

98 

Columbus,  Ohio 

237,031 

75 

Chicago  111 

2  701  705 

98 

Louisville  Kv 

234  891 

85 

Philadelphia  Pa 

1.  823'  799 

98 

St.  Paul,  Minn  

234,  595 

60 

Detroit  Mich 

993  678 

98 

Akron  6hio 

208,435 

98 

Cleveland  Ohio 

796  841 

98 

Omaha  Nebr 

191  601 

30 

St  Louis  'MO 

772*892 

92 

Worcester,  Mass    

179,  754 

65 

Boston  Mass 

748  060 

90 

Syracuse  N.  Y 

171,717 

66 

Baltimore  Md 

73'i'  v">fi 

98 

Richmond  V  a 

171  667 

97 

Pittsburgh   Pa 

.r>xv  .343 

95 

New  Haven,  Conn  

162,  537 

55 

Los  Angeles  Calif 

576  673 

86 

Memphis  Tenn 

162,  351 

50 

Buffalo  N.  Y. 

506,775 

100 

Dallas,  Tex  

158,  976 

70 

S»n  Franris^o  fialif 

506  676 

85 

Dayton,  Ohio  

152,  559 

95 

Milwaukee  Wis 

457  147 

98 

Houston  Tex 

138,296 

50 

Washington  D.C     . 

437  571 

91 

Hartford,  Conn  

138,036 

70 

Newark"  N  'j 

414  524 

80 

Grand  Rapids,  Mich... 

137,634 

90 

Cincinnati   Ohio 

401  247 

98 

Paterson  N  J 

135,  875 

80 

Minneapolis,  Minn 

380  582 

94 

Youngstown.  Ohio  

132,358 

92 

Kansas  Citv,  Mo 

324  410 

50 

Springfield  Mass 

129,614 

95 

Seattle  Wash 

315  312 

85 

New  Bedford  Mass 

121.217 

40 

Rochester,  N.  Y  

295.750 

65 

Fall  River,  Mass  

120,485 

55 

Portland,  Oreg      

2o>  2SS 

55 

Trenton   N.  J        

119,289 

60 

Denver  Colo 

256  491 

80 

Nashville  Tenn 

118,342 

40 

Providence.  R.  I.. 

237.  595 

60 

Salt  Lake  Citv.  Utah  .  .  . 

118,  110 

88 

8 


BULLETIN   342,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 


TABLE  3. — Approximate  quantity  of  mills  pasteurized  in  various  cities  as  shown 
by  returns  from  questionnaire  sent  in  1921 — Continued. 


City. 

Popula- 
tion, 1920 
census. 

Per  cent 
of  milk 
pas- 
teurized. 

City. 

Popula- 
tion, 1920 
census. 

Per  cent 
of  milk 
pas- 
teurized. 

Norfolk  Va.  . 

115,777 
113,344 
112,759 
111,  958 
110,  168 
107,784 
101,  177 
100,  176 
99,148 
98,  917 
95,283 
93,372 
93,091 
91,599 
91,558 
91,295 
88,723 
87,091 
85,264 
83,327 
78,384 
77,939 
77,560 
73,502 
70,983 
69,272 
67,  957 
67,327 
66,800 
65,651 
65,142 
61,903 
60,840 
60,331 
60,203 
59.316 
59,183 
58,593 
57,  895 
57,327 
56,378 
56,  208 
56,036 
55,593 
54,948 
53,844 
53,150 
52,548 
51,252 
50,842 
50,670 
50,022 
48,395 
48,374 
47,876 
45,566 
45,393 
44,  955 
44,  938 
44,616 
44,  255 
43,464 
43,050 
42,  726 
42,  515 
41,707 
41,611 
41,534 
41,534 
41,326 
41,013 
40,  472 
40,  296 
40,  120 
40,079 
39,675 
39,671 

range,  Eas 

50 
60 
34 
91 
66 
96 
65 
98 
75 
46 
87 
70 
85 
80 
70 
75 
36 
90 
80 
75 
75 
46 
33 
75 
90 
84 
100 
50 
75 
92 
50 
41 
80 
97 
75 
20 
94 
85 
80 
70 
100 
75 
82 
80 
70 
25 
50 
20 
8 
95 
95 
40 
50 
30 
63 
75 
33 
75 
45 
40 
15 
50 
55 
100 
60 
85 
33 
35 
14 
50 
13 
75 
90 
98 
20 
100 
60 

t  Orange  a 

San  Jose  Calif 

39,642 
39,  141 
37,  748 
37,  524 
37,295 
37,234 
36,  230 
36,  198 
36,192 
35,596 
35,000 
34,  764 
34,  273 
33,813 
33,162 
32,804 
31,017 
30,255 
30,  105 
30,  070 
29,053 
28,806 
28,  379 
28,064 
27,  824 
27,700 
27,644 
26,  341 
26,224 
25,202 
24,  057 
23,  594 
23,  127 
22,897 
22,779 
22,561 
22,486 
21,961 
21,  719 
21,  626 
21,  393 
21,284 
20,906 
20,  879 
20,  474 
20,292 
20,065 
19,861 
19,  653 
19,  516 
19,441 
19,  336 
19,  143 
18,661 
18,539 
18,060 
17,  734 
17,  677 
17,033 
17,004 
16,  971 
16,843 
15,  820 
15,  873 
15,868 
15,831 
15,  731 
15,  482 
15,  462 
15,  195 
15,  157 
15,100 
15,044 
14,648 
14,  375 
14,323 

3  village,  e 

70 
50 
88 
15 
99 
99.5 
90 
75 
15 
50 
95 
10 
50 
73 
25 
50 
75 
90 
85 
40 
25 
90 
40 
20 
80 
75 
75 
10 
80 
50 
30 
98 
33 
100 
30 
45 
90 
50 
15 
50 
7 
80 
65 
100 
85 
50 
50 
8 
100 
75 
20 
15 
70 
25 
80 
8 
90 
100 
50 
25 
20 
99 
12 
100 
10 
55 
10 
80 
20 
95 
40 
16 
50 
84 
50 
10 

ind  South 

Albany,  N.  Y  

Dubuque,  Iowa 

Brookline  Mass 

"The  Oranges"  i  N.  J  

Columbia,  S.  C.   . 

Wilmington,  Del  

Lorain  Onio 

Reading,  Pa'  

Evanston  111 

Kansas  City,  Kans  

Yonkers,  N.  Y  

Lynn,  M'ass  

•Dnliith.  Minn 

Elizabeth,  N.  J  

Newport  News,  v  a.  

Erie,  Pa  

PougnKeepsie,  IN  .  i  

Somerville,  Mass  

Flint,  Mich  

Jacksonville,  Fla  

Oklahoma,  Okla  

Ogden,Utah  

Canton,  Ohio  

Green  Bay,  Wis  
Newport,  R.I  

Honolulu,  Hawaii  
Manchester,  N.  H  
St.  Joseph,  Mo  
El  Paso,  Tex  
Allentown,  Pa  
South  Bend,  Ind  .  .  . 
Portland,  Me  

Colorado  Springs,  Colo  
Lynchburg,  Va  
Phoenix,  Ariz  
Alameda,  Calif  
Nashua,N.H  
Hagerstown,  Md  
Mansfield,  Ohio  

Plninfipld    N    J 

Charleston,  S.  C  
Johnstown,  Pa  
Binghamton,  N.  Y  
Rockford,  111  
Little  Rock,  Ark  
Saginaw,  Mich  
Springfield,  Ohio  
Altoona,  Pa  

Everett,  Wash  
Rome,N.Y  
Kearny,  N.  J  
Sioux  Falls,  S.  Dak  
Burlington,  Iowa  
Middletown,  Ohio  
Greenville,  S.  C  

Holyoke,  Mass  

Sandusky  ,  onio  
Burlington,  Vt  

Springfield  111 

Beverly,  Mass.'  

Racine,  Wis  

La  FayettMnd  

Chattanooga,  Tenn  

Fargo,  N.  Dak  
Durham,  N  .  C  

Gary  Ind 

Logansport,  Ind  

Wheeling  W  Va 

Boise,  Idaho  

Berkeley/Calif  

Beloit  Wis        

Long  Beach,  Calif  

Eau  Claire,  Wis  
Braddock,  Pa  

Haverhill  Mass 

Elyria,  Ohio  

Tucson,  Ariz  

Mason  City,  Iowa  

Tampa  Fla 

Greensboro,  N.  C  

Roanoke  Va 

Chicago  Heights,  111  

Niagara  Falls  N  Y 

Ann  Arbor,  Mich  

Topeka  Kans 

Santa  Barbara.  Calif  

Winston-Salem  N  C 

Dunkirk,  N.  Y  

Jackson  Mich 

Winona,  Minn  

Wausau,  Wis  

Yakima  Wash  

Elmira  N  Y' 

Alexandria,  Va  

Cicero  111 

Anniston,  •  Ala  

New  Castle,  Pa 

Hackensack,  N.  J  

Fresno  Calif 

Framingham,  Mass  

Galveston  Tex 

Ithaca  N  Y 

Montgomery  Ala 

Gardner,  Mass  

PuebFo  Colo 

Richmond  Calif  

Mt.  Vernon,N.  Y 

Corning,  N  .  Y  

Salem,  Mass 

Champaign,  111  

Perth  Am  boy,  N  .  j 

Peekskill,  N.  Y  

Butte,  Mont' 

ChilMcothe,  Ohio  

Lexington  Ky 

Marshalltown,  Iowa 

Pittsfield,  Mass 

North  Tonawanda,  N.  Y  

Lima,  Ohio 

Fitchburg,  Mass. 

Mishawaka  Ind           

Kenosha,  Wis 

Albuquerque  N  Mex 

Stockton,  Calif  

Billings  Mont                     

Everett,  Mass  

Wichita  Falls,  Tex  

Geneva  N  Y 

Hamilton.  Ohio  

Tiffin  Ohio 

Superior,  Wis  

Bridgeton,  N.  J 

1('The  Oranges"  include  O 
•Orange  township. 

nd  West  Orange,  South  Orang 

STATUS   OF   PASTEURIZATION    OF   MILK. 


TABLE  3. — Approximate  quantity  of  in  ilk  pasteurized  in  various  cities  as  shown 
&*/  returns  from  questionnaire  scut  in  1921 — Continued. 


City. 

Popula- 
tion, 1920 
census. 

Percent 
of  milk 
pas- 
teurized. 

City. 

Popula- 
tion, 1920 
census. 

Per  cent 
of  milk 
pas- 
teurized. 

Hiizh  Point,  X.  C 

14,302 
13,  f*04 
13,  722 
13,  521 
13,351 
13,294 
13,212 
13,  181 
13,104 
12,718 
12.548 
12,  456 
12,  451 
12,400 
12,  227 
11,996 
li;920 
11,634 
11,585 
11,475 
11,253 
10,968 
10,909 
10,790 
10,  476 
10.  42.-, 
10,  305 
10,  179 
10,  169 
10,  145 
10,  118 
9,901 
9,497 
9,474 

20 

50 

75 
5 
10 
65 
35 
50 
30 
25 
4 
10 
95 
95 
75 
7 
80 
66 
5 
45 
17 
50 
25 
15 
100 
75 
20 
60 
100 
65 
25 
95 
44 

Ashland,  Ohio    .. 

9,249 
9,130 
9,076 

8,849 
8.743 
8,664 

8,478 

7,'  435 
7,348 

7,348 
7,311 
7,272 
7,132 
7,096 
7,062 
7,016 
6,964 
6,757 
6,729 
6,011 
5,939 
5,917 
5,900 
5,8.82 
5  776 

70 
50 
GO 
50 
50 
30 
40 
23 
75 
25 
80 
75 
75 
56 
25 
25 
25 
30 
85 
50 
10 
50 
75 
25 
55 
50 
75 
100 
100 
10 
50 
45 
97 

1-villf1  Pa 

Chipnewa  Falls,  Wis 

Rochester  Minn 

Bedford  Ind 

Branch,  X.  J  

Warerville,  Me 

Wellsville,  Ohio.. 

Washington,  Ind 

Cortland  X   Y 

Hanover,  Pa 

Eureka,  Calif 

Mitchell,  S.  Dak 

Saratoga  X.  Y 

Manhattan.  Kans 

Cambridge,  Ohio  

DeKalb.Iil... 

Marquette,  Mich 

Salein,  X  .  J 

Morristown  N  J 

Marblehead,  Mass 

La  wreiice,  Kans  

Seymour,  Ind  

Xiles  Mich 

Vsburv  Park  X   J 

Painesville,  Ohio  
Princeton.  Ind  

Benton  Harbor,  Mich  

Tuscaloosa.  Ala 

Bemidji,  Minn 

Independence,  Kans 

Roswell  N.  Mex 

Martins  Ferrv,  Ohio  

Rumford  Falls.  Me 

Frankfort,  Ind 

Xewark,  N.  Y  ' 

Fairfield,  Coun 

Napa,  Calif  

Bristol.  Va 

Arkansas  Citv.  Kans  . 

Florence,  S.  C 

Medina,  N.  Y 

Plat  ts  burg  X   Y 

Ehvood,  Ind    

Princeton,  X  J 

Minot,  X.  Dak 

Palo  AJto  Calif 

Bucvrus,  Ohio  

Fredericksburg,  Va 

Salein.  Ohio  

Chic-kasha,  Okla 

Delphos  Ohio 

5,  745 
5,679 
4,236 
3,924 
2,440 
1,500 

Ilion,  X    Y 

St    \iarys  Ohio 

Whiting,  Ind 

Oberlin  Ohio 

Austin,  Minn 

Connersvilie,  Ind  

Rutherford,  X.  J 

Pullman,  Wash  

Davis,  Calif, 

Webster  drove,  Mo  

The  flash  process  consists  in  heating  rapidly  to  the  pasteurizing 
temperature,  then  cooling  quickly.  In  this  process  the  milk  is  heated 
from  30  seconds  to  1  minute  only,  usually  at  a  temperature  of  160° 
F.  or  above.  In  view  of  the  previously  mentioned  requirements  for 
pasteurized  milk  this  process  should  not  be  considered  suitable  for 
proper  pasteurization.  Several  cities  now  prohibit  the  use  of  the 
flash  process  for  the  pasteurization  of  milk. 

In  the  holder  process  the  milk  is  heated  to  temperatures  of  from 
140°  to  150°  F.  and  held  for  approximately  30  minutes,  after  which 
it  is  rapidly  cooled.  Sometimes  the  milk,  instead  of  being  held  at  a 
certain  temperature  in  one  tank  for  30  minutes,  is  merely  retarded 
in  its  passage  through  several  tanks  or  other  retarding  device  so  that 
the  length  of  time  required  for  the  milk  to  pass  through  is  about  30 
minutes.  In  such  cases,  however,  there  is  not  always  assurance  that 
all  the  milk  is  held  for  the  desired  time.  The  holder  process  has 
almost  entirely  replaced  the  flash  process,  and  is  the  one  most  used 
in  this  country. 

Pasteurization  in  bottles  is  the  latest  development  of  the  process 
to  be  used  on  a  practical  scale.  This  process,  as  first  practiced,  con- 
sisted in  putting  the  raw  milk  into  bottles  with  water-tight  seal  caps, 
107148°— 22 2 


10  BULLETIN   342,   U.   S.   DEPARTMENT   OF  AGRICULTURE. 

then  immersing  them  in  hot  water  until  heated  to  145°  F.  and  hold- 
ing them  at  that  temperature  for  from  20  to  30  minutes.  The  cool- 
ing was  accomplished  by  gradually  lowering  the  temperature  of  the 
water  until  that  of  the  milk  reached  50°  F. 

The  advantage  of  this  process  is  in  the  fact  that  the  milk  after 
heating  is  not  exposed  until  it  reaches  the  consumer,  thereby  elimi- 
nating any  danger  of  reinfection  with  disease-producing  organisms 
through  handling.  For  this  process  to  be  successful,  however,  it  is 
necessary  that  the  temperature  of  the  milk  in  bottles  be  measured  at 
the  bottom  of  the  bottle,  and  that  the  holding  period  of  30  minutes 
begin  when  the  temperature  at  the  bottom  has  reached  145°  F.  This 
is  essential,  because  the  milk  in  the  top  heats  faster  than  that  in 
the  bottom  of  the  bottle. 

The  matter  of  seals  is  also  important.  They  should  be  absolutely 
water-tight,  as  the  bottles  are  submerged  in  water,  and  during  cool- 
ing a  defective  cap  might  allow  infection  by  polluted  cooling  water. 
The  disadvantage  of  this  process  is  in  the  increased  cost  of  pasteuri- 
zation, caused  by  the  cost  of  the  seal  caps.  It  is  claimed,  however, 
that  the  saving  in  milk  losses  by  pasteurization  in  bottles  makes  up 
for  the  added  expense  of  caps.  It  is  now  possible  to  pasteurize  milk 
in  this  manner  without  using  water-tight  caps.  This  is  accomplished 
by  the  aid  of  devices  which  fit  over  the  tops  and  necks  of  the  bottles, 
thereby  protecting  the  ordinary  paper  caps  from  the  water  which  is 
sprayed  on  the  bottles  for  the  purpose  of  heating  or  cooling.  This 
method  of  protecting  the  tops  permits  the  use  of  the  ordinary  caps 
and  seems  to  remove  the  possible  danger  of  polluted  water  infecting 
the  milk. 

ADVANTAGES    OF    LOW-TEMPERATURE    PASTEURIZATION. 

In  general,  the  trend  of  pasteurization  has  been  toward  the  holder 
process,  and  with  this  tendency  the  use  of  lower  temperatures  has 
become  more  common.  As  a  general  rule,  when  the  holder  process 
is  used  milk  is  heated  to  about  145°  F.  for  from  20  to  30  minutes  and 
to  at  least  160°  F.  for  1  minute  when  the  flash  process  is  used.  From 
bacteriological,  chemical,  and  economical  standpoints  it  is  highly 
desirable  that  milk  be  pasteurized  at  the  lower  temperature. 

From  a  bacteriological  standpoint,  pasteurization  at  145°  F.  for 
30  minutes  gives  assurance,  so  far  as  we  know,  of  a  complete  de- 
struction of  nonspore-forming  disease-producing  bacteria  and  at 
the  same  time  leaves  in  the  pasteurized  milk  the  maximum  percent- 
age of  the  bacteria  that  cause  milk  to  sour  (lactic-acid  bacteria) 
and  only  a  small  percentage  of  those  that  cause  it  to  decompose 
(peptonizers).  When  higher  temperatures  are  used,  while  the  total 
number  of  all  kinds  of  bacteria  is  reduced,  the  percentage  of  lactic- 


STATUS   OF   PASTEURIZATION    OF   MILK.  11 

acid  bacteria  becomes  less  and  less  and  the  peptonizing  group  in- 
creases until  at  180°  F.,  or  above,  the  lactic-acid  bacteria  are  prac- 
tically destroyed  and  most  of  the  bacteria  left  belong  to  the  pep- 
tonizing  group.  The  heat-resistant  lactic-acid  bacteria  which  sur- 
vive pasteurization  at  145°  F.  for  30  minutes  play*  an  important 
role  in  the  souring  of  commercially  pasteurized  milk. 

From  a  chemical  standpoint,  the  advantage  of  the  lower  tempera- 
ture is  in  the  fact  that  milk  pasteurized  at  145°  F.  for  30  minutes 
does  not  undergo  any  appreciable  change  which  should  affect  its 
nutritive  value  or  digestibility.  According  to  Rupp  (26),  the  solu- 
ble phosphates  of  lime  and  magnesia  do  not  become  insoluble  and 
the  albumin  does  not  coagulate.  At  150°  F.  about  5  per  cent  of 
the  albumin  is  rendered  insoluble,  and  the  amount  increases  with 
higher  temperatures  to  160°  F.,  when  about  30  per  cent  of  the  al- 
bumin is  coagulated.  The  heating  period  in  Rupp's  experiments 
was  30  minutes. 

From  an  economic  standpoint  the  advantages  of  pasteurization 
at  low  temperatures  is  in  the  saving  in  the  cost  of  heating  and  cool- 
ing the  milk.  Bowen  (10)  has  shown  that  the  flash  process  of  pas- 
teurization requires  approximately  17  per  cent  more  heat  than  the 
holder  process.  There  is,  of  course,  a  correspondingly  wider  range 
through  -which  the  milk  must  be  cooled,  which  also  adds  to  the 
cost  of  pasteurization.  This  is  owing  to  the  fact  that  in  the  holder 
process  milk  may  be  heated  to  145°  F.  and  held  for  30  minutes, 
while  to  obtain  the  same  bacteriological  reduction  with  the  flash 
process,  with  one-minute  heating,  the  milk  would  have  to  be  heated 
to  165°  F.,  and  even  then  the  complete  destruction  of  disease-pro- 
ducing bacteria  might  be  questionable. 

TEMPERATURES  AND  METHODS  MOST  SUITABLE  FOR  PASTEUR- 
IZATION. 

In  view  of  the  advantages  of  the  lower  temperature  for  heating 
it  is  believed  that  the  temperature  of  pasteurization  should  be 
145°  F.  and  that  the  milk  should  be  held  at  that  temperature 
for  30  minutes.  It  has  been  found  that  heating  at  140°  F. 
for  that  length  of  time  will  destroy  pathogenic  bacteria,  provided 
all  the  milk  is  heated  to  that  point  and  held  the  full  length  of  time. 
But  it  has  been  shown  by  Schorer  and  Rosenau  (27)  that  it  is  diffi- 
cult to  do  this  under  commercial  conditions.  These  investigators 
tested  the  destruction  of  pathogenic  organisms  by  inoculating  milk 
with  B.  diphthei^ue,  B.  typhi,  and  B.  tuberculosis  and  pasteurizing 
it  in  100-gallon  lots  under  commercial  conditions.  They  found  that 


12  BULLETIN  342,   U.   S.  DEPARTMENT   OF  AGRICULTURE. 

sometimes  the  organisms  were  not  all  destroyed,  and  in  this  connec- 
tion state : 

Nothing  in  our  experiments  throws  any  doubt  upon  the  thermal  death  points 
of  the  microorganisms  tested.  We  are  sure  that  if  the  milk  reaches  140°  F. 
and  is  held  there  for  20  minutes  it  will  kill  tubercle,  typhoid,  and  diphtheria 
bacilli.  Our  experiments  show  that  milk  pasteurized  at  this  temperature  for  the 
specific  time  may  not  always,  in  practice,  reach  these  minimum  requirements. 
It  is  therefore  evident  that  a  liberal  factor  of  safety  is  necessary  in  the  opera- 
tion of  this  type  of  pasteurizer  under  commercial  conditions. 

They  state  further: 

Perhaps  the  best  temperature  to  meet  practical  conditions  is  145°  F.  and  the 
milk  should  be  held  from  30  to  45  minutes.  This  should  give  sufficient  leeway. 
If  the  pasteurizer  is  set  at  145°  F.  care  will  probably  be  taken  that  it  does 
not  go  above  148°  F.  on  account  of  destroying  the  cream  line,  and  it  is  not  likely 
that  the  mixed  milk  in  the  holding  tank  would  drop  below  140°  F.,  which  is 
the  minimum. 

Other  experiments  are  reported  by  Pease  and  Heulings  (in  the 
Report  of  the  Committee  on  Milk  Supply  of  American  Public  Health 
Association,  1920),  in  which  the  destruction  of  pathogenic  organisms 
was  tested  under  commercial  conditions  of  pasteurization.  Some  of 
the  pathogenic  types  were  found  living  after  heating  to  from  140° 
to  141°  F.  and  holding  for  15  minutes,  but  none  were  found  alive  after 
30  minutes'  holding.  Here  again  is  evidence  of  the  narrow  margin 
of  safety  when  milk  is  pasteurized  at  140°  F.  for  30  minutes,  and 
the  committee  expressed  the  following  opinion : 

The  committee  feels  that  while  enough  has  been  done  to  indicate  clearly  that 
a  proper  application  of  heat  to  a  temperature  of  140°  F.  for  a  minimum  period 
of  30  minutes  will  destroy  substantially  all  the  pathogenic  bacteria  in  milk, 
still  they  believe,  as  already  expressed,  that  a  margin  of  safety  for  biological 
reasons  calls  for  the  use  of  higher  temperatures  of  not  lower  than  145°  F. 

The  United  States  Department  of  Agriculture,  since  1910,  (2)  has 
advised  the  use  of  a  temperature  of  145°  F.  for  a  period  of  30  minutes 
for  the  pasteurization  of  milk.  Besides  insuring  an  ample  margin  of 
safety,  a  temperature  of  145°  F.  causes  a  considerably  greater  destruc- 
tion of  bacteria  in  milk  than  140°  F.  when  held  for  the  same  period 
of  30  minutes. 

Extensive  experiments  (3)  in  the  research  laboratories  of  the 
Dairy  Division  have  shown  that  the  thermal  death  point  of  a  con- 
siderable number  of  bacteria  lies  between  140°  and  145°  F.;  there- 
fore an  increase  of  5°  above  140°  F.  produces  a  great  increase  in  the 
destruction  of  bacteria. 

There  is  a  marked  tendency  in  commercial  work  to  pasteurize  at 
or  near  the  minimum  temperature  requirement  necessary  to  destroy 
pathogenic  organisms,  namely,  140°  F.  Such  seems  to  be  the  case 
because  of  the  fear  of  injuring  the  cream  line.  In  fact,  the  opinion 
is  often  expressed  by  milk-plant  operators  that  a  temperature  of 


STATUS  OF  PASTEURIZATION   OF   MILK.  13 

145°  F.  can  not  be  used  because  of  the  marked  loss  in  cream  line. 
Harding  (19)  has  studied  the  effect  of  temperature  on  the  cream  line 
in  a  number  of  different  plants  throughout  the  country,  and  has  come 
to  the  following  conclusion : 

The  data  here  presented  show  that  the  volume  of  cream  on  milk  begins 
measurably  to  decrease  when  the  temperature  of  pasteurization  rises  from  142° 
F.  to  144°  F.  As  the  temperature  goes  higher,  the  decrease  in  the  volume  of 
cream  becomes  rapidly  more  pronounced ;  at  145°  F.  it  amounts  to  slightly  more 
than  10  per  cent  by  volume;  at  146°  F.  it  amounts  to  1C.6  per  cent;  and  at 
148°  F.,  to  approximately  40  per  cent. 

It  may  be  said,  however,  that  there  are  plants  in  this  country,  in- 
cluding some  of  the  largest,  in  which  milk  is  successfully  pasteurized 
at  145°  F.,  and  this  temperature  is  maintained  for  30  minutes.  It  is 
also  interesting  to  note  that  at  the  1921  meeting  of  the  International 
Dairy  and  Milk  Inspectors'  Association,  Pease  reported  experiments 
carried  on  by  Heulings  and  him  which  showed  that  pasteurization  at 
145°  F.  for  30  minutes  did  not  decrease  the  cream  line  when  the  milk 
was  properly  heated  and  cooled. 

The  method  of  pasteurization,  whether  it  is  the  holder  or  in-the- 
bottle  process,  is  not  so  important  provided  the  process  is  such  that 
the  milk  is  heated  to  145°  F.  and  that  all  of  it  is  held  for  30  minutes. 
The  great  majority  of  plants  pasteurize  by  the  holder  process,  and  it 
is  gratifying  to  observe  that  the  flash  process  is  but  little  used. 
Replies  to  a  questionnaire  sent  to  numerous  cities  in  this  country 
showed  only  33  plants  using  the  flash  process  in  18  cities  out  of  the 
266  which  supplied  information  on  this  subject.  Five  cities  reported 
that  the  flash  process  was  not  allowed,  while  one  permitted  its  use 
but  would  not  allow  the  milk  to  be  labeled  " Pasteurized."2 

SUPERVISION  OF  THE  PROCESS. 

Intelligent  supervision  of  the  pasteurizing  process  is  absolutely 
necessary  and  can  not  be  provided  unless  there  is  a  thorough  knowl- 
edge of  the  primary  object  of  pasteurization  and  the  bacteriological 
principles  involved. 

The  primary  object  is  the  destruction  of  any  disease-producing 
bacteria  which  may  be  in  the  milk  and  the  handling  of  the  pasteurized 
milk  in  such  manner  that  it  can  not  be  reinfected.  When  this  object 
is  accomplished  it  is  found  that  a  large  percentage  of  the  bacteria 
in  the  milk  are  destroyed  and  its  keeping  quality  greatly  unproved. 

The  primary  object  can  be  accomplished  by  heating  all  the  milk  to 
145°  F.  and  holding  it  for  a  period  of  30  minutes.  It  is  then  only 
necessary  to  cool  the  milk  immediately  over  thoroughly  cleaned  and 

2  For  information  on  pasteurizing  equipment  the  reader  is  referred  to  United  States 
Department  of  Agriculture  Bulletin  No.  890,  Milk-Plant  Equipment. 

107148°— 22 3 


14  BULLETIN  342,   U.  S.  DEPARTMENT  OF  AGRICULTURE. 

steamed  coolers,  to  run  into  thoroughly  cleaned  and  steamed,  or  other- 
wise sterilized,  bottles  through  a  thoroughly  cleaned  and  sterilized 
bottle  filler,  then  to  cap  the  bottles  with  sterilized  caps  and  place  the 
milk  in  low-temperature  refrigerators. 

This  process  sounds  relatively  simple,  yet  at  every  step  problems  are 
encountered  which  may  defeat  the  primary  object. 

First  of  all,  it  must  be  kept  in  mind  that  bacteria  are  too  small  to 
be  seen  by  the  naked  eye  and  that  they  are  distributed  in  the  air  of 
the  milk  plant,  upon  the  equipment  with  which  milk  comes  in  contact, 
and  upon  the  hands  of  employees.  Flies  also  carry  millions  of  bac- 
teria. When  milk  comes  to  the  plant  to  be  pasteurized  the  logical 
thing  to  do  is  to  see  that  it  comes  in  contact  only  with  apparatus 
which  has  been  thoroughly  cleaned  and  thoroughly  steamed.  The 
equipment  may  appear  clean,  but  since  bacteria  can  not  be  seen 
with  the  naked  eye,  a  clean  (to  the  eye)  tank  or  pipe  may  contain 
many  millions.  Means  must  be  taken  to  destroy  as  many  of  them  as 
possible.  To  do  this  steam  is  usually  employed,  for  steam  at  205°  F. 
or  above  for  a  period  of  2  to  5  minutes  will  destroy  disease-producing 
bacteria  and  all  but  spores  of  the  harmless  types.  Equipment  so 
treated  may  be  called  bacteriologically  clean,  but  must  be  visibly 
clean  before  application  of  the  steam  if  satisfactory  results  are  to  be 
expected. 

When  the  equipment  is  in  this  condition,  the  milk  can  be  pasteur- 
ized. At  this  point  the  object  is  to  heat  all  the  milk  to  145°  F.  and 
hold  it  for  30  minutes.  In  intelligent  supervision  many  problems 
are  encountered  at  this  step  in  the  process.  They  are  well  dis- 
cussed in  a  paper  entitled  Pasteurization  of  Milk,  which  is  a  report 
of  the  Committee  on  Milk  Supply  of  the  Sanitary  Engineering  Sec- 
tion of  the  American  Public  Health  Association,  1920.  Briefly,  the 
principal  points  are : 

1.  Heat  all  the  milk  to  145°  F. 

2.  Hold   all  the  milk  for  30  minutes.     (Some  continuous-flow  systems  do 
not  do  this.) 

3.  Watch  for  leaking  valves,  also  pipe  lines  which  hold  milk  below  the  pas- 
teurizing temperature. 

4.  Have  accurate  recording  thermometers  so  arranged  as  to  show  the  total 
heating  period.    Recording  thermometers  should  be  frequently  checked  against 
a  standard  thermometer  of  unquestionable  accuracy. 

5.  Watch  for  foam  on  the  milk.    This  may  stay  in  the  vats  for  hours  at  a 
warm  temperature  suitable  for  bacterial  development. 

After  proper  heating  and  holding,  the  pathogenic  organisms  have 
been  destroyed  and  the  total  number  of  bacteria  reduced  to  a  mini- 
mum point.  The  next  problem  is  to  cool  and  bottle  the  milk  with- 
out reinfection,  particularly  with  disease-producing  bacteria. 


STATUS  OF   PASTEURIZATION   OF   MILK.  15 

To  do  this,  bacteriologically  clean  coolers,  bottle  fillers,  bottles, 
and  sterilized  caps  are  necessary ;  and  what  is  of  greatest  importance 
is  to  see  that  the  pasteurized  milk  does  not  come  in  contact  with 
human  hands,  or  with  apparatus,  including  bottles  and  caps,  touched 
by  the  hands  after  being  sterilized.  The  hands  of  milk  handlers 
constitute  perhaps  the  most  dangerous  source  of  reinfection  in  the 
plant,  for  they  may  convey  pathogenic  organisms.  Through  such 
channel  milk  may  be  contaminated  by  carriers  of  many  diseases. 

In  order  to  guard  against  such  possibilities,  all  employees  who 
handle  apparatus  or  milk  in  the  plant  or  during  delivery  should 
undergo  frequent  medical  examination,  and  any  diseased  persons 
or  carriers  should  be  prevented  from  working  in  positions  in  which 
they  have  even  indirect  contact  with  milk,  milk  equipment,  or  deliv- 
ery of  the  product. 

It  is  perhaps  unnecessary  to  say  that  flies  are  also  a  very  serious 
menace  to  the  milk  supply.  They  must  be  kept  out  of  milk  plants, 
for  it  is  impossible  to  tell  when  they  may  infect  the  milk.  This  in- 
fection can  occur  directly  by  flies  getting  into  the  milk  or  indirectly 
through  contamination  of  equipment  or  containers. 

At  every  step  in  the  pasteurization  of  milk,  one  is  compelled  to 
think  of  the  process  in  terms  of  bacteria  in  order  to  supervise  it 
intelligently. 

HANDLING  MILK  AFTER  PASTEURIZATION. 

Pasteurization  of  milk  destroys  about  99  per  cent  of  the  bacteria ; 
consequently  the  milk  is  not  sterile.  On  account  of  this  fact,  pas- 
teurized milk  is  still  a  perishable  product,  and  must  be  handled 
with  the  same  care  as  raw  milk.  This  is  a  point  for  both  the  con- 
sumer and  the  milkman  to  remember. 

Milk  after  pasteurization  should  be  cooled  to  about  40°  F.  and 
kept  at  that  temperature  until  delivery.  During  warm  weather  it 
should  be  iced  on  the  delivery  wagons.  From  a  sanitary  standpoint 
all  milk,  whether  raw  or  pasteurized,  should  be  delivered  as  soon  as 
possible,  in  order  that  the  consumer  may  get  it  in  the  best  condition. 
In  the  best  pasteurized  milk,  when  held  at  about  40°  F.,  there  is  only 
a  slight  bacterial  increase  during  the  first  24  hours.  In  many  cases 
the  pasteurization  and  delivery  may  be  so  arranged  that  the  con- 
sumer gets  the  milk  before  much,  if  any,  change  has  taken  place  in 
the  bacterial  content.  For  the  benefit  of  the  consumer  the  word 
"  Pasteurized  "  should  be  printed  on  the  cap,  as  it  is  only  right  for 
him  to  know  whether  he  is  using  raw  or  pasteurized  milk.  Some  people 
object  to  pasteurized  milk,  especially  for  infant  feeding,  while  others 
desire  it.  It  has  been  the  experience  of  numerous  milk  dealers  that 
the  labeling  of  their  product  has  greatly  increased  their  trade. 


16  BULLETIN  342,  U.  S.  DEPARTMENT  OF  AGRICULTURE. 

COST  OF  PASTEURIZING  MILK. 

The  present  cost  of  pasteurization  has  been  estimated  by  Bo  wen 
from  the  cost  given  in  his  earlier  paper  (10)  on  the  assumption  that 
the  average  price  of  coal  has  increased  2.04  times  and  that  milk- 
plant  labor  and  equipment  have  increased  50  per  cent  over  the  prices 
of  1913,  the  year  in  which  his  paper  was  written.  He  obtained  the 
information  from  a  series  of  tests  in  five  establishments  which  were 
considered  to  represent  the  average  city  milk  plant.  The  pasteuriz- 
ing equipment  in  each  consisted  of  a  heater,  a  holding  tank,  a 
regenerator,  and  a  cooler.  The  cost  of  operation  was  based  on  the 
pasteurizing  cycle,  starting  with  the  initial  temperature  of  the  raw 
milk  and  raising  it  to  the  pasteurizing  temperature,  then  cooling  to 
the  initial  temperature  of  the  raw  milk.  He  based  the  costs  on  daily 
interest  at  6  per  cent  per  annum  on  capital  invested  in  pasteurizing 
equipment,  and  depreciation  and  repairs  per  day  at  25  per  cent 
per  annum;  interest  per  day  at  6  per  cent  per  annum  on  capital 
invested  in  mechanical  equipment  for  pasteurizing,  such  as  engines, 
boilers,  etc.,  and  depreciation  and  repairs  per  day  at  10  per  cent  per 
annum.  Other  costs  figured  were  labor,  coal  now  estimated  at  $8.16 
a  ton,  cooling  water  now  estimated  at  $0.75  per  1,000  cubic  feet,  and 
refrigeration  now  estimated  at  $2  a  ton.  With  these  new  estimates 
substituted  for  the  old  figures,  Bowen  calculates  that  the  average 
cost  of  pasteurizing  1  gallon  of  milk  is  approximately  $0.0049,  or  a 
little  less  than  one-half  cent. 

BACTERIA  WHICH  SURVIVE  PASTEURIZATION. 

It  has  been  stated  that  about  99  per  cent  of  the  bacteria  in  milk 
are  destroyed  by  pasteurization;  consequently  about  1  per  cent  of 
the  bacteria  remain  alive,  and  the  kinds  left  depend  entirely  on  the 
temperature  to  which  the  milk  is  heated  and  the  number  of  heat- 
resistant  bacteria  in  the  milk.  From  studies  of  the  bacteria  which 
survive  pasteurization,  it  is  possible  to  show  graphically  the  hypo- 
thetical relations  of  the  bacterial  groups  in  raw  milk  and  in  milk 
pasteurized  by  the  holder  process  at  various  temperatures  under 
laboratory  conditions. 

The  bacterial  flora  of  the  various  kinds  of  milk  is  represented  in 
Figure  1  by  columns  of  equal  length  divided  into  sections,  which,  in 
a  general  way,  show  the  relative  proportion  of  the  bacterial  groups. 

From  the  figure  it  may  be  seen  that  raw  milk  contains  four  prin- 
cipal groups  of  bacteria — the  acid,  inert,  alkali,  and  peptonizing. 
The  acid  group  is  divided  again  into  two — the  acid-coagulating, 
which  coagulates  milk  within  14  days,  and  the  acid  group,  which 
merely  produces  acid  and  does  not  coagulate  it  in  less  time  than  that. 
In  raw  milk  the  inert  group  is  the  largest. 


STATUS   OF   PASTEURIZATION   OF   MILK. 


17 


In  milk  pasteurized  at  145°  F.  the  great  increase  in  the  proportion 
of  the  acid-coagulating  and  acid  groups  is  plainly  shown.  The  per 
cent  of  the  alkali  and  peptonizing  groups  is  reduced.  At  160°  F. 
the  total-acid  group  is  still  the  largest,  but  the  acid-coagulating 
group  is  made  up  of  bacteria  which  coagulate  very  slowly.  At  this 


•    '62.e°c. 


7€7°C.       82.2°C. 


93.3 


FIG.  1. — The  hypothetical  relation  of  the  bacterial  group  to  raw  and  pasteurized  milk. 

temperature  the  alkali  group  is  greatly  reduced,  and  the  peptonizing 
reduced  to  the  minimum.  At  170°  F.  the  total-acid  group  remains 
about  the  same,  but  the  organisms  produce  acid  and  coagulate  the 
milk  very  slowly.  The  alkali  group  is  practically  destroyed  although 


18  BULLETIN  342,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 

occasionally  a  sample  may  show  a  fairly  high  per  cent.  The  most 
important  change  is  in  the  peptonizing  group.  At  this  temperature 
the  ratio  of  this  group  to  the  total  number  of  bacteria  begins  to 
increase.  The  increase  when  milk  is  pasteurized  at  180°  F.  is  even 
more  striking.  At  this  temperature  more  than  75  per  cent  of  the 
bacteria  which  survive  are  peptonizers.  No  organisms  of  the  acid- 
coagulating  group  are  found,  and  only  a  small  per  cent  of  the  acid 
group.  Occasionally  a  few  of  the  alkali  group  may  be  found.  At 
190°  F.  and  200°  F.  the  bacterial  groups  which  survive  are  about  the 
same  in  their  relative  sizes  as  at  180°  F. 

It  is  very  evident  that  when  the  bacterial  flora  of  pasteurized  milk 
is  under  Discussion  the  temperature  of  the  process  is  of  fundamental 
importance.  From  Figure  1  the  bacterial  groups  left  in  milk  pas- 
teurized at  different  temperatures  may  be  seen  at  a  glance.  It  must 
be  remembered,  however,  that  the  relations  of  the  bacterial  groups 
represent  only  average  conditions  and  that  the  bacterial  flora  of  every 
sample  of  milk  must  not  be  expected  to  conform  exactly* to  these 
averages.  Variations  in  methods  and  conditions  in  the  production  of 
milk  may  considerably  influence  the  bacterial  group  relations  of  an 
individual  sample. 

The  results  in  Figure  1  may  perhaps  be  better  explained  in  popular 
terms.  When  milk  is  pasteurized  at  145°  F.  for  30  minutes,  most 
of  the  bacteria  .  (lactic-acid)  left  alive  in  it  are  of  the  kind  which 
cause  it  to  sour,  and  there  are  present  only  a  few  bacteria  (pep- 
tonizing) which  cause  it  to  decompose.  As  the  milk  stands,  the  acid 
formers  grow  and  cause  the  milk  to  sour  instead  of  decompose. 
When  milk  is  pasteurized  at  180°  F.  for  30  minutes,  however,  the  bac- 
teria (lactic-acid)  which  cause  the  souring  of  milk  are  practically  all 
destroyed,  and  those  which  are  alive  (peptonizing)  continue  to  grow 
and  cause  the  milk  to  decompose. 

Not  only  do  certain  types  of  lactic- acid  bacteria  survive  pas- 
teurization but  some  also  grow  at  the  pasteurizing  temperature. 
Sometimes  upon  long-continued  heating  at  140°  to  145°  F.  for 
several  hours,  milk  sours  in  the  holding  tanks  due  to  the  growth 
of  these  organisms.  The  ordinary  period  of  holding  does  not  provide 
sufficient  time  for  their  development,  so  this  type  of  souring  is  not 
encountered  in  milk  plants  except  when  there  is  an  interruption 
in  the  pasteurizing  process  due  to  some  abnormal  condition. 

SURVIVAL  OF  STREPTOCOCCI. 

Since  the  general  groups  of  bacteria  which  survive  pasteuriza- 
tion have  been  discussed,  let  us  now  consider  a  more  specific,  group. 
It  has  been  the  custom  of  some  authorities  to  consider  the  presence 
of  streptococci  in  pasteurized  milk  an  indication  of  an  ineffective 
process.  As  already  pointed  out,  pathogenic  streptococci  are  readily 


STATUS   OF   PASTEURIZATION    OF    MILK.  19 

destroyed  by  proper  pasteurization.  In  a  study  of  the  subject  (4), 
however,  it  was  found  that  certain  strains  of  streptococci  are  able 
to  survive  pasteurizing  temperatures. 

The  thermal  death  points  of  139  cultures  of  streptococci  isolated 
from  cow  feces.  from  the  udder  and  mouth,  and  from  milk  and  cream, 
showed  a  wide  variation  when  the  milk  was  heated  for  30  minutes 
under  conditions  similar  to  pasteurization.  At  140°  F.,  the  lowest 
pasteurizing  temperature,  89  cultures,  or  64.03  per  cent,  survived; 
at  145°  F.,  the  usual  temperature  for  pasteurizing,  46,  or  33.07  per 
cent,  survived;  and  at  160°  F.,  3  cultures,  or  2.16  per  cent,  survived; 
all  these  were  destroyed  at  165°  F.  The  streptococci  from  the  udder, 
on  the  whole,  were  less  resistant  and  those  from  milk  and  cream 
more  resistant  to  heat  than  those  from  the  mouths  and  feces  of 
the  cows. 

Two  classes  of  streptococci  seem  to  survive  pasteurization:  (1) 
Streptococci  which  have  a  low  majority  thermal  death  point  (the 
temperature  at  which  a  majority  of  the  bacteria  are  killed),  but 
among  which  a  few  cells  are  able  to  survive  the  pasteurizing  tem- 
perature. This  ability  of  a  few  bacteria  may  be  due  to  certain 
resistant  characteristics  peculiar  to  them  or  it  may  be  caused  by 
some  protective  influence  in  the  milk.  (2)  Streptococci  which  have 
a  high  majority  thermal  death  point,  and  which,  when  such  is  the 
case,  survive  because  this  point  is  above  the  temperature  of  pas- 
teurization. This  ability  to  resist  destruction  by  heating  is  a  per- 
manent characteristic  of  certain  strains  of  streptococci. 

These  streptococci  which  have  a  high  thermal  death  point  above 
the  pasteurizing  temperature  undoubtedly  play  an  important  part 
in  the  occasional  high  counts  found  in  pasteurized  milk.  Such 
counts  are  sometimes  observed  when  the  count  of  the  raw  milk  runs 
the  same  as  usual.  As  the  proportion  of  these  heat-resistant  types 
vary  in  milk  their  numbers  may  at  times  reach  such  figures  that 
their  survival  of  the  pasteurizing  process  gives  an  abnormally  high- 
count  product.  The  presence  and  variation  of  their  numbers  in  milk 
therefore  is  a  matter  which  must  be  given  consideration  in  connec- 
tion with  bacteria  standards  for  pasteurized  milk. 

It  is  evident  that  certain  varieties  of  streptococci  are  able  to  survive 
pasteurization,  while  others  are  probably  always  destroyed.  Numer- 
ous investigators  have  studied  the  thermal  death  point  of  streptococci 
isolated  from  patients  having  septic  sore  throat  and  have  found  that 
the  organism  was  destroyed  by  pasteurization  at  145°  for  20  minutes. 
These  results,  together  with  the  protection  which  proper  pasteuriza- 
tion seems  to  afford  against  epidemics  of  that  disease  caused  by  milk 
supplies,  indicate  that  the  varieties  of  streptococci  associated  with  or 
responsible  for  the  disease  are  among  the  varieties  which  have  a  low 
thermal  death  point. 


20  BULLETIN  342,   U.   S.  DEPARTMENT   OF  AGRICULTURE. 

THE  COLON  TEST  FOR  EFFICIENCY  OF  PASTEURIZATION. 

In  a  study  (6)  of  the  ability  of  colon  bacilli  to  survive  pasteuriza- 
tion it  was  found  that  certain  strains  could  survive  pasteurization  at 
145°  F.  for  30  minutes.  On  examining  174  cultures  of  colon  bacilli  it 
was  found  that  at  140°  F.,  the  lowest  pasteurizing  temperature,  95 
cultures  survived;  at  145°  F.,  the  usual  temperature  for  pasteuriza- 
tion, 12  survived.  In  each  case  the  heating  period  was  30  minutes. 
Considerable  variation  was  observed  in  the  thermal  death  point  of 
the  colon  bacilli  which  survived  at  145°  F.  When  the  cultures  which 
withstood  the  first  heating  were  again  heated  it  was  found  that  many 
did  not  survive,  and  in  each  subsequent  heating  different  results 
were  obtained.  Colon  bacilli  have  a  low  majority  thermal  death 
point  but  on  account  of  the  resistance  of  a  few  cells,  they  may  survive 
the  pasteurizing  process. 

The  colon  test  as  an  index  of  the  efficiency  of  the  process  of 
pasteurization  is  complicated  by  the  ability  of  certain  strains  to 
survive  a  temperature  of  145°  F.  for  30  minutes  and  to  develop 
rapidly  when  the  pasteurized  milk  is  held  under  certain  tempera- 
ture conditions  met  during  storage  and  delivery.  Consequently 
the  presence  of  a  few  colon  bacilli  in  pasteurized  milk  under  ordi- 
nary market  conditions  does  not  necessarily  indicate  that  the  milk 
was  not  properly  heated.  The  presence  of  a  large  number  of  colon 
bacilli  immediately  after  the  heating  process  indicates  that  the  milk 
has  not  been  heated  to  145°  F.  for  30  minutes  and  the  test  properly 
applied  should  be  valuable  in  control  work.  Fermentation  tubes 
can  be  used  for  making  the  test,  but  when  gas  formation  is  noted 
the  presence  of  colon  bacilli  should  be  demonstrated  by  further  tests. 
Often  anaerobic  spore  formers  are  encountered  which  survive  pas- 
teurization and  give  the  typical  fermentation  tube  test. 

PAST   AND    PRESENT    THEORIES    OF    PASTEURIZATION. 

•pksteiiHzatlo^i  at  present^  looked  upon  with  favor  by  medical 
men,  sanitarians,  dairymen,  and  consumers,  but  the  art  has  not  been 
developed  without  opposition,  and  its  value  is  not  universally  ac- 
cepted. Most  of  the  objections  to  pasteurized  milk  have  been  based 
on  theory  or  on  experiments  in  which  the  milk  was  pasteurized  at 
high  temperatures.  In  view  of  our  modern  theories  they  are  of  no 
great  importance. 

One  of  the  greatest  objections  to  pasteurized  milk  has  been  that 
the  heating  destroyed  the  lactic-acid  bacteria  and  that  putrefactive 
organisms  were  left,  which,  when  relieved  from  the  restraining  action 
of  the  acid-forming  bacteria,  would  develop,  forming  toxins  and 
putrefactive  products.  It  was  believed  that  the  milk,  because  it 
was  not  sour,  would  be  consumed  in  that  condition.  This  objection 


STATUS  OF  PASTEURIZATION   OF   MILK.  21 

was  based  on  experiments  in  which  milk  was  heated  to  temperatures 
near  the  boiling  point  and  can  not  be  applied  to  milk  pasteurized  at 
low  temperatures.  From  the  results  of  many  years'  work  in  the 
Dairy  Division  on  commercial  pasteurized  milk,  it  has  been  found 
that  such  milk  sours,  as  raw  milk  does,  but  that  the  souring  is 
delayed  when  compared  with  the  souring  of  the  same  grade  of  raw 
milk.  Pasteurized  milk  sours  in  a  manner  similar  to  that  of  a  high 
grade  of  raw  milk,  and  there  is  no  more  reason  to  fear  the  over- 
growth of  putrefactive  organisms  than  there  is  in  any  high-grade 
milk.  Pasteurization  for  30  minutes  at  temperatures  of  about  145° 
F.,  as  is  generally  practiced  in  this  country,  does  not  destroy  all 
the  lactic-acid  organisms,  and  those  which  survive  play  an  important 
role  in  the  souring  of  commercially  pasteurized  milk. 

Another  objection  to  pasteurized  milk  has  been  that  bacteria  grow 
faster  in  it  than  in  raw  milk.  In  spite  of  several  experiments  which 
seem  to  prove  this  point,  it  has  never  been  thoroughly  established. 
It  has  been  found  that  the  rate  of  bacterial  increase  is  approximately 
the  same  when  the  comparison  is  made  between  raw  milk  and  pasteur- 
ized milk  having  about  the  same  bacterial  content. 

It  is  often  stated  that  pasteurization,  even  if  it  does  destroy 
bacteria,  does  not  destroy  poisonous  products  of  their  growth.  This 
can  hardly  be  considered  a  real  objection,  for  if  they  are  present  in 
raw  milk  they  must  be  consumed  with  it,  and  if  pasteurization  does 
not  destroy  them  the  pasteurized  milk  would  be  no  worse  than  raw 
milk. 

The  question  as  to  whether  pasteurization  destroys  beneficial 
enzyms  is  still  an  open  one.  In  the  light  of  our  present  knowledge 
of  the  enzyms  in  milk  and  the  part  they  play  in  the  digestive  process 
it  is  quite  impossible  to  settle  the  question  of  their  importance.  It 
is  evident,  however,  that  the  low  temperatures  now  in  use  in  pasteuri- 
zation have  little  effect  on  the  commonly  recognized  enzyms. 

The  opponents  of  pasteurization  have  raised  an  objection  on  the 
ground  of  its  direct  influence  on  the  milk  producer.  It  has  been 
asserted  that  pasteurization  would  cause  lax  methods  of  production 
on  the  farm,  for  the  reason  that  farmers  would  know  that  the  milk 
was  to  be  pasteurized  and,  therefore,  they  could  be  careless  in  its  pro- 
duction. There  seems  to  be  some  basis  for  this  objection,  but  in  any 
city  where  there  is  any  inspection  of  the  raw-milk  supply  the  same 
inspection  can  and  should  be  continued  even  though  the  milk  is  to 
be  pasteurized. 

From  a  chemical  standpoint  ^serious  objections  have  been  raised 
against  pasteurized  milk,  because  the  heating  produces  changes  which 
render  the  milk  less  digestible,  particularly  in  the  case  of  infants. 
As  has  already  been  stated,  however,  Rupp  (26)  has  found  that  milk 


22  BULLETIN  342,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 

pasteurized  at  145°  F.  for  30  minutes  does  not  undergo  any  appreci- 
able chemical  change.  He  found  that  soluble  phosphates  do  not 
become  insoluble,  that  the  albumin  does  not  coagulate,  and  that  when 
higher  temperatures  are  used  chemical  changes  do  occur.  He  also 
developed  the  fact  that  5  per  cent  of  the  albumin  is  rendered  insoluble 
in  milk  heated  for  30  minutes  at  150°  F.,  while  at  160°  F.  30.78  per 
cent  of  the  albumin  is  coagulated.  Further  evidences  that  low-tem- 
perature pasteurization  does  not  injure  the  digestibility  and  nutritive 
value  of  milk  are  shown  by  the  results  of  feeding  experiments  with 
babies.  According  to  Weld  (31),  a  number  of  babies  that  were  fed 
raw  milk  and  pasteurized  milk  showed  only  a  slight  difference  in 
the  average  net  daily  gain  in  weight  during  the  feeding  period.  The 
slight  difference  was  in  favor  of  pasteurized  milk.  Hess  (21),  how- 
ever, has  found  that  milk  pasteurized  for  30  minutes  at  145°  F.  may 
cause,  in  infants,  a  mild  form  of  scurvy,  which  yields  readily  to  so 
simple  a  remedy  as  orange  juice. 

High-temperature  pasteurization  of  earlier  days  must  not  be  con- 
fused with  low -temperature  pasteurization  of  the  present  day.  Many 
of  the  objections  which  have  been  raised  to  pasteurization  have  been 
founded  on  the  observation  of  milk  heated  to  high  temperatures. 
The  fallacy  of  the  objections  to  pasteurization  have  been  shown, 
however,  through  scientific  research  in  the  last  few  years,  and  as  a 
result  the  value  of  the  process  has  been  firmly  established. 

PASTEURIZATION   AND   VITAMINS. 

The  discovery  of  vitamins  within  recent  years  has  shown  how  im- 
possible it  is  to  estimate  nutritive  requirements  solely  in  terms  of 
digestible  protein,  carbohydrate,  fat,  and  inorganic  salts.  But  little 
is  known  of  the  real  chemical  nature  of  vitamins,  except  that  they  are 
necessary  for  normal  growth  and  health.  Three  vitamins  are  now 
recognized,  known  as  vitamin  A  (soluble  in  fat)  and  vitamins  B 
and  C  (soluble  in  water).  Most  authorities  now  agree  that  fat- 
soluble  A  and  water-soluble  B  are  essential  for  growth,  and  water- 
soluble  C,  the  antiscorbutic  vitamin,  may  also  play  a  part  in  this 
relation. 

Because  of  the  limited  character  of  the  infant's  diet  the  vitamin 
content  of  its  food  is  more  important  than  that  of  the  adult's,  as  the 
latter  has  a  great  variety  of  foods.  Fortunately,  milk  has  been 
found  to  be  a  food  containing  the  three  vitamins  and  the  effect  of 
pasteurization  on  the  vitamin  content  is  of  importance. 

Fat-soluble  A  and  water-soluble  fe  have  been  found  to  be  quite 
resistant  to  heat,  and  it  is  agreed  that  pasteurization  has  little  or 
no  effect  upon  them.  The  antiscorbutic  vitamin  C,  however,  is  quite 
sensitive  to  heat  above  122°  F.  While  the  destruction  of  this  vita- 


STATUS  OF  PASTEURIZATION  OF  MILK.  23 

min  depends  upon  the  temperature,  length,  and  condition  of  heat- 
ing, as  well  as  the  reaction  of  the  material  in  which  it  exists,  there 
seems  to  be  little  doubt  that  pasteurization  of  milk,  under  usual  com- 
mercial conditions,  at  145°  F.  for  30  minutes,  weakens  the  antiscor- 
butic property  of  the  milk. 

Hess  and  Fish  (20),  in  1914,  in  studying  scurvy  in  children  found 
that  some  cases  of  scurvy  developed  when  milk  was  used  which  had 
been  pasteurized  at  145°  for  30  minutes. 

After  further  studies  on  this  subject  Hess  (22)  made  the  following 
statement : 

Although  pasteurized  milk  is  to  be  recommended  on  account  of  the  security 
which  it  affords  against  infection,  we  should  realize  that  it  is  an  incomplete 
food.  Unless  antiscorbutics,  such  as  orange  juice,  the  juice  of  an  orange  peel, 
or  potato  water  is  added,  infants  will  develop  scurvy  on  this  diet.  This  form 
of  scurvy  takes  some  months  to  develop  and  may  be  termed  subacute.  It  must 
be  considered  not  only  the  most  common  form  of  this  disorder,  but  one  which 
passes  most  often  unrecognized.  In  order  to  guard  against  it,  infants  fed  ex- 
clusively on  a  diet  of  pasteurized  milk  should  be  given  antiscorbutics  far  earlier 
than  is  at  present  the  custom,  even  as  early  as  the  first  month  in  life. 

In  the  course  of  the  development  of  infantile  scurvy,  growth  both  in  weight 
and  in  length  is  markedly  affected.  Under  these  conditions  weight  ceases  to 
increase,  and  a  stationary  plane  is  maintained  for  weeks  or  for  months.  There 
is  quick  response,  however,  on  the  administration  of  orange  juice  or  its  equiva- 
lent ;  indeed  sapergrowth  is  thereupon  frequently  manifested. 

PASTEURIZED   MILK   FOR  INFANTS.  • 

A  rational  view  must  be  taken  of  the  use  of  pasteurized  milk. 
Shall  the  protection  against  infection,  which  is  made  available  by 
the  proper  pasteurization  of  milk,  be  discarded  because  of  its  defi- 
cient antiscorbutic  property,  or  shall  its  protection  be  accepted  and 
the  deficiency  in  vitamin  C  be  made  up  by  feeding  orange  juice  or 
other  antiscorbutics  ? 

Perhaps  the  feeding  of  infants  calls  for  even  further  thought  than 
is  generally  given.  As  Eddy  (14)  in  his  recent  book  points  out,  there 
are  two  points  to  be  kept  in  mind  in  infant  nutrition.  The  first  is 
that  the  vitamin  content  of  cow's  or  human  milk  is  dependent  pri- 
marily on  the  food  eaten  by  the  producer  of  the  milk.  In  other 
words,  milk  is  merely  a  mobilization  of  vitamins  eaten,  and  if  the 
diet  is  to  yield  a  milk  rich  in  vitamins  the  food  eaten  must  also  be 
rich.  He  further  points  out  the  fact  that  cereals  are  poor  in  vitamins 
and  green  grasses  rich  in  them,  and  that  this  brings  up  the  question 
of  winter  feeding  if  the  milk  supply  is  used  for  infants,  and  he  sug- 
gests that  the  variability  in  vitamins  A  and  B  in  milk  may  at  times 
make  it  necessary  to  supplement  the  diet. 

The  second  point  brought  out  by  Eddy  expresses  what  appears  to 
be  the  most  reasonable  attitude  toward  the  use  of  pasteurized  milk 


24  BULLETIN  342,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 

for  infant  feeding  according  to  our  present  knowledge  of  vitamins, 
and  it  is  therefore  quoted : 

The  second  point  in  regard  to  milk  lies  in  the  effect  of  pasteurization.  This 
measure  is  now  well-nigh  universal  and  in  America  at  least  has  played  a  tre- 
mendous part  in  the  reduction  of  infant  mortality,  especially  in  the  summer 
months.  At  present,  however,  we  know  that  this  treatment  while  removing 
dangerous  germs  may  also  eliminate  the  antiscorbutic  factor.  The  sensible 
attitude  then  is  to  recognize  this  fact  and  if  a  clean  whole  milk  is  not  available 
retain  the  pasteurization  and  meet  the  vitamin  deficiency  by  other  agents. 
Such  agents  are  orange  juice  and  tomato  juice,  and  experience  has  already 
shown  that  these  juices  can  be  well  tolerated  by  infants  much  earlier  than 
used  to  be  thought  possible. 

It  seems,  therefore,  that  the  only  serious  effect  of  pasteurization 
on  the  vitamins  is  on  the  antiscorbutic  vitamin  C,  and  it  is  evident 
that  the  feeding  of  orange  or  tomato  juice,  or  other  antiscorbutic, 
readily  makes  up  for  the  deficiency  of  this  vitamin  in  pasteurized 
milk. 

THE  NECESSITY  FOR  PASTEURIZATION. 

The  need  for  safeguarding  the  milk  supply  is  amply  proved  by 
the  numerous  epidemics  traced  to  milk.  Trask  (29)  reported  179 
epidemics  of  typhoid  fever  from  1881  to  1907,  of  which  107  were  in 
the  United  States,  51  epidemics  of  scarlet  fever,  including  25  in  this 
country,  during  the  same  period,  and  23  epidemics  of  diphtheria 
from  1879  to,  1907,  including  15  in  the  United  'States.  These  were 
all  traced  to  milk.  He  also  listed  7  epidemics  of  sore  throat,  most 
of  which  occurred  in  England.  Since  1907  several  epidemics  of 
septic  sore  throat  have  been  traced  to  milk.  Among  these  may  be 
mentioned  the  epidemics  at  Boston,  Chicago,  and  Baltimore,  and 
others  which  have  occurred  in  smaller  cities. 

The  problem  of  pasteurization  is  not  based  simply  on  the  question 
of  which  is  preferable,  raw  or  pasteurized  milk,  but  rather  upon  the 
most  economical  and  practical  way  of  producing  a  safe  milk  supply. 

In  connection  with  the  possibility  of  transmission  of  disease 
through  the  agency  of  milk,  certain  fundamental  facts  must  be 
recognized. 

1.  That  such  possibilities  exist  as  demonstrated  by  epidemics  of  the  past. 

2.  That  certain  diseases  transmitted  to  man,  such  as  tuberculosis,  may  come 
from  diseased  animals.    The  danger  from  this  source  can  be  prevented  by  the 
elimination  of  tuberculous  cattle  from  producing  herds  on  the  basis  of  the 
tuberculin  test. 

3.  That  the  freeing  of  the  herds  from  tuberculosis  offers  no  protection  against 
other  diseases,  as  typhoid  fever,  diphtheria,  and  septic  sore  throat,  because  the 
pathogenic  organisms  causing  these  diseases  may  come  from  infected  water  sup- 
plies or  probably  in  most  cases  from  human  carriers  of  disease. 

The  term  "carriers"  is  used  to  designate  persons  who  carry  the 
disease-producing  bacteria.  In  the  case  of  diphtheria,  carriers  har- 


STATUS  OF  PASTEURIZATION   OF   MILK.  25 

bor  the  diphtheria  organisms  and  discharge  them  from  the  nose  or 
throat.  Typhoid  carriers  discharge  typhoid  bacilli  in  their  feces  or 
urine.  Diphtheria  carriers  may  become  so  after  having  an  acute 
attack  of  the  disease  or  from  other  carriers.  Typhoid  carriers  are 
particularly  important,  because  from  2  to  4  per  cent  of  the  persons 
who  have  had  typhoid  fever  continue,  as  evidence  shows,  to  discharge 
the  typhoid  bacilli  in  their  feces  or  urine  or  both  and  become  chronic 
carriers. 

Persons  suffering  from  sore  throat  are  a  menace  to  the  milk 
supply,  and  probably  the  organisms  responsible  for  septic  sore  throat 
are  sometimes  carried  in  the  throat  of  apparently  normal  individuals. 

It  is  manifestly  impossible  to  have  a  medical  examination  of  all  per- 
sons engaged  in  producing  and  handling  milk.  Yet  such  examinations 
at  frequent  intervals  would  be  necessary,  together  with  tuberculin 
testing  and  the  assurance  of  unpolluted  water  supplies  on  every  farm, 
in  order  to  safeguard  the  milk  supply  of  the  Nation  to  the  same 
extent  that  is  now  possible  by  proper  pasteurization.  The  apprecia- 
tion of  the  need  for  pasteurization  is  distinctly  shown  by  the  marked 
increase  in  pasteurization  in  the  United  States. 

REFERENCES  TO  LITERATURE. 

ANDERSON,  A.  K.,  and  FINKELSTEIN,  K. 

(1)  1919.     A  study  of  the  electro-pure  process  of  treating  milk.     In  Jour. 

Dairy  Science,  v.  2,  no.  5,  p.  374-406. 
AYEBS,  S.  H.,  and  JOHNSON,  W.  T.,  jr. 

(2)  1910.     The  bacteriology  of  commercially  pasteurized  and  raw  market 

milk.     U.  S.  Dept.  Agr.,  Bur.  Anim.  Indus.  Bui.  no.  126. 

(3)  1913.    A  study  of  the  bacteria  which  survive  pasteurization.     U.  S. 

Dept.  Agr.,  Bur.  Anim.  Indus.  Bui.  no.  161. 

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Dept.  Agr.,  Jour.  Agr.  Research,  v.  2,  no.  4,  p.  321-330. 

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(6)  1915.    Ability  of  colon  bacilli  to  survive  pasteurization.    In  U.   S. 

Dept.  Agr.,  Jour.  Agr.  Research,  v.  3,  no.  5,  p.  401-410. 
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(7)  1918.    The  thermal  death  point  and  limiting  hydrogen  ion  concentra- 

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(10)  1914.    The  cost  of  pasteurizing  milk  and  cream.    U.  S.  Dept.  Agr., 

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26  BULLETIN  342,   U.   S.   DEPARTMENT  OF  AGRICULTURE. 

BEAT,  H.  A. 

(11)  .1915.    A  milk  borne  epidemic  of  tonsillitis  in  tuberculous  patients. 

In  Jour.  Amer.  Med.  Assoc.,  v.  64,  no.  14,  p.  1127-1130. 
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(12)  1912.    The  Chicago  epidemic  of  streptococcus  sore  throat  and  its  re- 

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(13)  1918.    The  relation  of  streptococci  to  bovine  mastitis  and  septic  sore 

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Md. 
EVANS,  ALICE  C. 

(15)  1916.    The  bacteria  of  milk  freshly  drawn  from  normal  udders.     In 

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